BACKGROUND: Fecal incontinence is a devastating condition with few US Food and Drug Administration-approved pharmacologic treatment options. Loperamide and psyllium, both first-line treatments, have different mechanisms of action without any comparative data. OBJECTIVE: The purpose of this study was to examine the effectiveness and tolerability of loperamide compared with psyllium for reducing fecal incontinence. We hypothesized that psyllium fiber supplementation would be more effective than loperamide for reducing fecal incontinence episodes and have fewer adverse effects. DESIGN: We conducted a randomized, double-blind, placebo-controlled crossover trial comparing loperamide (followed by psyllium) with psyllium (followed by loperamide). SETTINGS: Our sites included outpatient clinics within a Veterans Affairs medical center and university affiliate. PATIENTS: Participants included community-dwelling adults (n = 80) with at least 1 fecal incontinent episode on a 7-day bowel diary. INTERVENTION: Participants received either daily loperamide (plus placebo psyllium powder) or psyllium powder (plus loperamide placebo) for 4 weeks. After a 2-week washout, participants crossed over to 4 weeks of alternate treatment. MAIN OUTCOME MEASURES: The primary outcome was the number of fecal incontinence episodes from 7-day bowel diaries. Secondary outcomes included symptom severity, quality of life, and tolerability. RESULTS: Mean age was 60.7 ± 10.1 years; 68% were men. After determining nonsignificant carryover effects, combined analyses showed no differences between the loperamide and psyllium groups for reducing fecal incontinent episodes, symptom severity, or quality of life. Within each group, both loperamide and psyllium reduced fecal incontinent episodes and improved symptom severity and quality of life. Constipation occurred in 29% of participants for loperamide vs 10% for psyllium. LIMITATIONS: Limitations include the washout period length and dropout rate after crossing over to the second intervention. CONCLUSIONS: Both loperamide and psyllium improve fecal incontinence. Loperamide was associated with more adverse effects, especially constipation.